towlower
========

POSIX specification: http://www.opengroup.org/onlinepubs/9699919799/functions/towlower.html

Gnulib module: wctype

Portability problems fixed by Gnulib:

  * This function is missing on some platforms: IRIX 5.3, Solaris 2.5.1.

  * This function returns values of which the upper 16 bits are incorrect on some platforms: mingw.

Portability problems not fixed by Gnulib:

  * On AIX and Windows platforms, wchar_t is a 16-bit type and therefore cannot accommodate all Unicode characters.